With increases in worldwide energy consumption, economic and environmental issues linked to fossil fuel extraction and use are becoming more pressing. Concerns surrounding the security of global crude oil supplies and of global warming, in particular, have drawn attention to carbon fuels produced from biomass. In the long term, with oil resources becoming more expensive to develop, the chemical industry will need new sources for carbon-based raw materials, which could be provided by biomass.
One of the most specific and versatile routes to produce fuels or other bio-products is to obtain monosaccharides from biomass. These monosaccharides can be converted to fuels or bioproducts by, for example, fermentation (Dodds D R. et al., Science 318:1250-1251, (2007)) or catalytic processes (Huber G. et al., Science 308:1446-1450 (2005); Romén-Leshkov Y. et al., Nature 447:982-985 (2007)). However, selectively producing sugars from lignocellulosic biomass is challenging and typically involves several stages. The initial or “pretreatment” stage consists of partially extracting the hemicellulose and/or lignin fraction of biomass. Pretreatment increases access to catalytic sites for cellulase and xylanase enzymes, which are added during the second (i.e., hydrolysis) stage to depolymerize cellulose and any remaining hemicellulose. In the pretreatment process, care needs to be taken to minimize the degradation of hemicellulose, which is a polymer of mostly pentose and some hexose sugars.
Various pretreatment approaches have included using acid or base solutions or simply pure water (often at higher temperatures) to deconstruct hemicellulose and lignin (Mosier N. et al., Bioresource Technology 96:673-686 (2005)); Wyman C. et al., Bioresource Technology 96:2026-2032 (2005); Wyman C. et al., Bioresource Technology 96:1959-1966 (2005); Wyman C. et al., Biotechnology Progress 25:333-339 (2009)). Some of these technologies involve either flowing the reacting media through the biomass (Gupta R. et al., Biotechnology Progress 25 (2009); Liu C. et al., Applied Biochemistry and Biotechnology 113:977-987 (2004) or an explosive decompression of the total mixture in the case of steam explosion (Bura R. et al., Biotechnology Progress 25:315-322 (2009)) or ammonia fiber explosion (AFEX) (Balan V. et al., Biotechnology Progress 25:365-375 (2009); Teymouri F. et al., Bioresource Technology 96:2014-2018 (2005)). The chemically catalyzed systems are generally environmentally unfriendly and costly, while hot water systems suffer from mass-transfer and dilution issues while demanding significant amounts of energy. These problems have been addressed by, for example, recycling the chemical catalysts or developing packed bed biomass reactors to increase mixing. However, these processes still generally suffer from a high degree of complexity, high cost, low sugar yields (i.e., low efficiencies), and significant production of undesired byproduct, such as those based on furfural.
Moreover, the biomass conversion processes currently in use generally suffer from a significant lack in versatility in being able to process a wide range of different biomass materials under substantially the same conditions with the same equipment. On the contrary, conventional practice generally requires the use of significantly different equipment and/or processing conditions for processing different types of biomass (e.g., hardwood vs. perennial grasses). This significant limitation in current biomass conversion technologies presents a major hindrance in making biomass-to-energy technology competitive with conventional energy production and usage. The ability to apply a single process for any of a wide variety, or mixture, of biomass materials provides the significant advantage of producing useful materials and energy from any biomass that may become available, whether it be indigenous or non-indigenous to the area in which the biomass conversion facility is located.